The "Ellipse Tool" works much like the Rectangle Tool. The only difference is that since there are no corners, you will need to guess where the corners would be in order to place your ellipse where you want it to go. Imagine that the ellipse you are drawing is being "hugged" by a rectangle that goes around it. Like up the top-most and left-most peaks of the ellipse's curve to guess where the corner of the imaginary rectangle is and click there. Then, drag down to where the bottom-most and right-most peaks of the ellipse's curve would be, and click again. Your ellipse should be about the right size and in the right position if you estimated it correctly. It can take some practice.

The Ellipse Tool draws outline ellipses. The interior of the outline ellipse is transparent.